The present invention relates to a propelling drive transmission structure for a walking operator type lawn mower having a main frame supporting a cutting blade housing, and particularly to a transmission structure comprising a vertically adjustable drive axle disposed rearwardly of the blade housing, an engine disposed above the blade housing for driving the drive axle, and a change speed device for effecting change speed on the drive axle.
This type of lawn mower is capable of cutting grass at a selected height by vertically adjusting the drive axle.
One such lawn mower is disclosed in Japanese Utility Model Publication (Kokai) No. 60-157282. In this known construction, the change speed device is operatively connected to the drive axle by a transmission belt. A variation in spacing between the change speed device and the drive axle resulting from a vertical adjustment of the drive axle is absorbed by a flexion of the transmission belt. The change speed device is disposed at a higher level than the blade housing, thereby to minimize the length of a transmission line from the engine to the change speed device and to minimize influences of the vertical adjustment of the drive axle.
The above conventional construction, however, has room for improvement in that drive transmission may be impaired by grass clippings. For example, grass clippings scattering in the course of a grass cutting operation tend to adhere to the belt and cause slips between the belt and pulleys.